1. Field of the Invention
The present invention relates to a tire for a motor vehicle, in particular to a pneumatic tire whose tread pattern provides excellent off-road and on-road performance.
2. Description of the Prior Art
In the present specification, the term “all terrain” tire will be used for indicating a tire for both a two or four wheel drive motor vehicle to be used, according to circumstances, on asphalted roads as well as on non-asphalted roads (e.g. on snow- or mud-covered roads, or on grassy, sandy or gravelly surfaces).
Generally, off-roads vehicles are designed for pure and extreme off-road, for instance for driving on rough surfaces, on snow-covered roads, on muddy or sandy surfaces.
In the last years, all terrain motor vehicles (particularly four wheel drive, briefly “4×4”), i.e. vehicles which combine off-road and on-road performance, have become more and more popular and at present their versatility is highly appreciated by the market. Among such all terrain vehicles are, for instance, the PICK-UPs as well as the so called SUVs (Sport Utility Vehicles) which combine the characteristics of comfort and roominess typical of a station wagon with high performance (especially in terms of high torques and high speeds) typical of high-powered cars.
The overall performance of pneumatic tires to be mounted on all terrain motor vehicles is a peculiar issue of the tire manufacturers and very difficult to be achieved. In fact, the drivers of said vehicles ask for tires providing both good off-road performance and good on-road handling properties, while ensuring that low noise level and good wear resistance are obtained.
However, these requirements are mainly conflicting each other. Therefore, the tires which have been produced to date normally represent a compromise of the required performance mentioned above and do not reach the highest performance levels which can be obtained with a tire specifically designed for on-road or off-road use only.
Generally, a tread pattern is provided with large and deep circumferential grooves for discharging the water collected in the tire foot-print area in order to avoid the occurrence of the well-Known and hazardous aquaplaning effect while running on wet surfaces. On the contrary, in tires specifically designed for driving on dry surfaces, the number and width of longitudinal and transverse grooves is preferably reduced in order to increase the tread wear resistance, to reduce the tread noise level during running of the tire and to provide a smooth ride.
Furthermore, for safe and good driving on snow-covered surfaces, a tread pattern is generally provided with a plurality of sipes and small notches in order to suitably trap the snow since the snow-on-snow friction is greater than the rubber-on-snow friction.
Moreover, it is generally known to provide a tread pattern with a plurality of shoulder and central blocks in order to increase the tire off-road performance while running on uneven surfaces, e.g. on rough roads.
A tire for off-road motor vehicles is known, for instance, from EP 0 841 198 in the name of the same Applicant of the present application. The tire tread band according to EP 0 841 198 comprises: at least two longitudinal grooves substantially parallel to each other and extending circumferentially on opposite sides of the tire equatorial plane; at least one series of transverse grooves crossing the longitudinal grooves, said transverse and longitudinal grooves delimiting at least two rows of shoulder blocks circumferentially distributed at the opposite side edges, and at least one row of central blocks disposed between said rows of shoulder blocks, each of said transverse grooves comprising at least two transverse channels which mutually meet to give said transverse groove an axially continuous course extending between opposite side edges of the tread band. Each of said transverse channel comprises: an outer end stretch extending from the respective side edge of the tread band in an orientation substantially perpendicular to the equatorial plane; a curvilinear connecting stretch that, by joining to the corresponding curvilinear connecting stretch of the laterally-opposite transverse channel, gives said transverse groove said continuous course. At least one of said transverse channels further comprises an inner end stretch penetrating into a respective block of said central blocks, said connecting stretch interconnecting said outer end stretch with said inner end stretch in a continuity relationship.